This invention relates in general to telecommunication switching complexes having a plurality of interconnected switching systems, and more particularly to the program control structure within such switching systems.
Telephone switching systems have evolved to include various forms of computerized common controls of the programmable stored program variety. Conventionally, the computerized controls have been configured as multi-task monoprocessors with the result being the need to coordinate relatively complex control tasks and memory configurations. One of the characteristics of the monoprocessor approach is the need for an executive program or an executive processor for controlling system operations. Typically this results in a program which is interrupt driven, thereby requiring a potentially complex heirarchy for the various interrupts. Moreover it is generally necessary to queue work for the purpose of distributing the real time work load of the processor. The resultant complexity of the programming task will be apparent from the foregoing, not only as it applies to initially generating and debugging the programs, but also in maintaining the system should a fault develop.
The present invention is related to and has particular utility when used in conjunction with the telecommunication switching system control as described in U.S. Pat. No. 4,256,926 entitled "Microprocessor Control Complex For A Telecommunication Switching System" and U.S. Pat. No. 4,259,549 entitled "Dialed Number To Function Translator for Telecommunications Switching System Control Complex" the disclosures of which are incorporated herein by reference thereto. The former-mentioned patent discloses a multiprocessor control for distributing call processing tasks while the latter referenced patent discloses the manner in which the various processors, and in particular the data base processor, systematically operates to translate dialed numbers into operational functions to perform all the switching system functions. With such a control the call processing functions are distributed among the processors in the system in such a way as to modularize the control functions and simplify the programming.
The patents are addressed to a single switching system configuration including the processor control hardware implementation and the processor memory architecture. The invention disclosed herein is primarily concerned with the particular structure of the data base memory stores in guiding the common control to effect an efficient intercommunication of dialed directory numbers between remotely located communication switching systems when such systems are interconnected to form a telecommunications switching complex.
A switching complex finds a wide variety of applications where, for instance, a business organization occupies remote locations, each location having a switching system (such as a PBX) servicing users who have a need to communicate with many other users. The switching systems of the complex are typically interconnected by conventional tie trunks to provide communication paths between the systems so that users serviced by any one system may communicate with users serviced by another switching system within the complex.
Traditionally, the communication with a station (extension telephone) resident in and thus serviced by another system is invoked by first going off-hook, receiving dial tone, dialing a trunk access code (such as the digit "9"), and after having received a second dial tone from the distance switching system, dialing the directory number of the destination station. While station users are able to communicate across remote switching systems in this manner, the users are required to perform some operations which should more aptly be carried out by the modern sophisticated switching systems. Such operations include; remembering whether the dialed station is nonresident, dialing the trunk access code and proceeding with the station number dial upon receipt of the destination dial tone.
It is thus evident that communications between switching systems of a complex are conventionally carried out by the traditional user-initiated action and reaction to signalling stimuli and that the common control data base information of each system is not shared to the extent possible. As a consequence, station users are instrumental in deciding the course of action that must be taken in order to effectuate communications through multiple switching systems. Owing to the fact that the switching systems of the traditional communication complex communicate therebetween by standard telephone signalling methods, the telephone users must have some of the information and exercise some of the decision making aspects to complete calls across the various switching systems.
In view of the fact that modern telecommunications switching systems involve state-of-the-art computer data processing technologies, it should be feasible to incorporate such decisional aspects within the switching systems rather than relying on the users to remember them. Because of the sizeable capital investments required in establishing a switching complex, such a complex and its respective switching systems could be utilized to a fuller extent and made more efficient by programming the common controls to recognize when dialing across the switching systems is requested and to take the appropriate action to effect such a result with minimal knowledge thereof by the users.
The related patents as hereinbefore referenced, discuss the ability of a single switching system to share its hardware among separate groups of stations, where stations in each group may have the same directory numbers, all without confusing one station in one group with another station in another group. Such a provision of "customer groups" is highly desirable, however this aspect has heretofore been accomplished only with single switching system environments.
It is a paramount object of the present invention to provide means for streamlining the intercommunications between a plurality of communication switching systems of a switching complex so that the complex as a whole functions more systematically rather than as autonomous interconnected systems.
It is a primary object of the present invention to provide a switching system having the capability of automatically transferring a dialed number to the destination switching system servicing the associated station so that the switching function desired by the user is effected, all without the user being aware that another system is involved.
As a corollary to the foregoing, it is an object of the present invention to provide a memory structure and data organization in the switching system controls such that a user requesting service of a remote switching system need not remember access codes or incur long delays in waiting for dial tones.
An important feature of the invention is to provide switching systems, such as PBXs, which may be interconnected in a daisy-chained fashion such that a dialed number is continually forwarded to the destination system in which the station, corresponding to the dialed number, is resident. From all appearances to the user of the system, he has his own private system and is unaware, except for a small delay, of the number of intermediate PBX's which forwarded the dialed number.
A further advantage is to provide a switching complex having switching systems interconnected in such a manner so as to maintain the integrity of customer groups throughout the complex.
The foregoing as well as other objects and advantages of the present invention will become apparent from the detailed description of the invention which follows hereinafter, and when considered together with the appended drawings.
While the invention will be described in connection with certain embodiments presently considered to be preferred, there is no intent to limit it to these embodiments. On the contrary, the intent is to cover all alternatives, modifications and equivalents included within the spirit and scope of the invention as defined by the appended claims.